Wireless power receiver

ABSTRACT

An automatic tuning assist circuit is coupled with a transmission antenna. Multiple switches SW and a first auxiliary capacitor CA are arranged between a first terminal and a second terminal of the automatic tuning assist circuit. A first control unit is configured to switch on and off the multiple switches SW in synchronization with a driving voltage V DRV . A power supply is configured to apply the driving voltage V DRV  across a series circuit that comprises the transmission antenna and the automatic tuning assist circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/093,241, filed on Nov. 29, 2013, the entirecontents of which are incorporated herein by reference and priority towhich is hereby claimed. Application Ser. No. 14/093,241 is theContinuation of application No. PCT/JP2012/003190, filed May 16, 2012.Priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is herebyclaimed from Japanese Application No. 2011-124443, filed Jun. 2, 2011and Japanese Application No. 2011-128661, filed Jun. 8, 2011, thedisclosures of which are both also incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless power supply technique.

2. Description of the Related Art

In recent years, wireless (contactless) power transmission has beenreceiving attention as a power supply technique for electronic devicessuch as cellular phone terminals, laptop computers, etc., or forelectric vehicles. Wireless power transmission can be classified intothree principal methods using an electromagnetic induction, anelectromagnetic wave reception, and an electric field/magnetic fieldresonance.

The electromagnetic induction method is employed to supply electricpower at a short range (several cm or less), which enables electricpower of several hundred watts to be transmitted in a band that is equalto or lower than several hundred kHz. The power use efficiency thereofis on the order of 60% to 98%. In a case in which electric power is tobe supplied over a relatively long range of several meters or more, theelectromagnetic wave reception method is employed. The electromagneticwave reception method allows electric power of several watts or less tobe transmitted in a band between medium waves and microwaves. However,the power use efficiency thereof is small. The electric field/magneticfield resonance method has been receiving attention as a method forsupplying electric power with relatively high efficiency at a middlerange on the order of several meters (A. Karalis, J. D. Joannopoulos, M.Soljacic, “Efficient wireless non-radiative mid-range energy transfer”ANNALS of PHYSICS Vol. 323, January 2008, pp. 34-48)

FIG. 1 is a diagram showing a wireless power transmission systemaccording to a comparison technique. The wireless power transmissionsystem 1 r includes a wireless power transmitting apparatus 2 r and awireless power receiving apparatus 4 r. The wireless power transmittingapparatus 2 r includes a transmission coil L_(TX), a resonance capacitorC_(TX), and an AC power supply 10 r. The wireless power receivingapparatus 4 r includes a reception coil L_(RX), a resonance capacitorC_(RX), and a load 70.

The resonance frequency is an important factor in magnetic field(electric field) resonance power transmission. The resonance frequencyof the transmitter side LC resonance circuit is represented byf_(TX)=1/(2π√(L_(TX)·C_(TX))). The resonance frequency of the receiverside LC resonance circuit is represented byf_(RX)=1/(2π√(L_(RX)·C_(RX))). Thus, in order to provide high-efficiencyelectric power transmission, there is a need to appropriately adjust thetransmitter-side and receiver-side resonance frequencies and thefrequency of the AC power supply 10 r. However, in actuality, suchresonance frequencies fluctuate depending on various kinds of factors.It is difficult for the power receiving apparatus side to tune thefluctuating resonance frequency based on the magnetic field (or electricfield) itself as it has been transmitted from the power supplyapparatus. This is because, in some cases, the resonance frequencydetected by the power receiving apparatus side further changes dependingon the resonance frequency and the phase conditions of the powerreceiving apparatus side.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve such a problem.Accordingly, it is an exemplary purpose of an embodiment of the presentinvention to provide a wireless power transmitting apparatus, a wirelesspower receiving apparatus, and a wireless power supply system, which arecapable of automatically tuning the resonance frequency.

An embodiment of the present invention relates to a wireless powertransmitting apparatus configured to transmit an electric power signalcomprising any one from among an electric field, a magnetic field, andan electromagnetic field to a wireless power receiving apparatus. Thewireless power transmitting apparatus comprises: a transmission antennacomprising a transmission coil; an automatic tuning assist circuitcoupled with the transmission antenna; and a power supply configured toapply an AC driving voltage across a series circuit that comprises thetransmission antenna and the automatic tuning assist circuit. Theautomatic tuning assist circuit comprises: a first terminal; a secondterminal; N (N represents an integer) auxiliary capacitors; multipleswitches; and a first control unit. Each of the multiple switches isarranged between two terminals from among the first terminal, the secondterminal, and the terminals of the N auxiliary capacitors. The firstcontrol unit is configured to switch on and off the multiple switches insynchronization with the driving voltage.

When the frequency of the driving voltage does not match the resonancefrequency of the resonance circuit including the transmission antenna,the resonance circuit functions as a capacitor circuit or otherwise aninductor circuit. In this case, in the transmission antenna, a resonancecurrent is induced with a phase that is delayed or otherwise advancedwith respect to the phase of the driving voltage. In this state, in acase in which the first switch and the second switch are switched on andoff in synchronization with the driving voltage and with a predeterminedphase difference with respect to the driving voltage, the firstauxiliary capacitor is charged or otherwise discharged so as to providephase matching between the resonance current and the driving voltage. Byapplying the correction voltage that develops at the first auxiliarycapacitor to the transmission antenna, such an arrangement provides aquasi-resonant state. Such an embodiment is capable of automaticallytuning the transmission antenna with respect to the driving voltage evenwithout an operation such as adjusting the capacitance of the resonancecapacitor. It should be noted that, in the present specification, the“phase difference” may be set to zero. That is to say, examples of the“phase difference” state include a phase matching state.

Also, the first control unit may be configured to switch on and off eachof the multiple switches with the same frequency as that of the drivingvoltage, or otherwise with a frequency obtained by multiplying ordividing the frequency of the driving voltage by an odd number.

Also, the automatic tuning assist circuit may comprise: a first switchand a first auxiliary capacitor arranged in series between the firstterminal and the second terminal; and a second switch arranged betweenthe first terminal and the second terminal such that it is arranged inparallel with the first switch and the first auxiliary capacitor.

Also, the first control unit may be configured to switch on and off thefirst switch and the second switch with the same frequency as that ofthe driving voltage, and with a given phase difference with respect tothe driving voltage.

Also, the automatic tuning assist circuit may further comprise a secondauxiliary capacitor between the first terminal and the second terminalsuch that it is arranged in series with the second switch.

With such an arrangement, the second auxiliary capacitor is charged orotherwise discharged so as to provide phase matching between theresonance current and the driving voltage, in addition to charging orotherwise discharging the first auxiliary capacitor. Such an arrangementis capable of providing a quasi-resonant state.

The first control unit may be configured to switch on and off the firstswitch and the second switch with the same frequency as that of thedriving voltage, and with a given phase difference with respect to thedriving voltage.

Also, the first switch and the second switch may each be configured as auni-directional switch. Also, the first control unit may be configuredto switch on and off the first switch and the second switch with a phasecontrolled such that no current flows through each of their inverselyconducting elements.

Also, the first switch and the second switch may each be configured as abi-directional switch. Such an arrangement is capable of relaxing thephase constraints on the switching operation.

Also, the automatic tuning assist circuit may be coupled in series withthe transmission antenna via a transformer.

With an embodiment, the power supply may comprise: a DC power supply;and a first high-side switch and a first low-side switch sequentiallyarranged in series between an output terminal of the DC power supply anda fixed voltage terminal. Also, the transmission antenna and theautomatic tuning assist circuit may be coupled in series between thefixed voltage terminal and a connection node that connects the firsthigh-side switch and the first low-side switch.

With an embodiment, the power supply may comprise: a DC power supply; afirst high-side switch and a first low-side switch sequentially arrangedin series between an output terminal of the DC power supply and a fixedvoltage terminal; and a second high-side switch and a second low-sideswitch sequentially arranged in series between the output terminal ofthe DC power supply and the fixed voltage terminal. Also, thetransmission antenna and the automatic tuning assist circuit may becoupled in series between a connection node that connects the firsthigh-side switch and the first low-side switch and a connection nodethat connects the second high-side switch and the second low-sideswitch.

Also, the transmission antenna may comprise a resonance capacitorarranged in series with the transmission coil.

Also, the power supply may be configured to apply an AC driving voltagevia a transformer between respective terminals of a circuit thatcomprises the transmission antenna and the automatic tuning assistcircuit.

Another embodiment of the present invention relates to a wireless powersupply system. The wireless power supply system comprises: a wirelesspower transmitting apparatus according to any one of the aforementionedembodiments; and a wireless power receiving apparatus configured toreceive an electric power signal from the wireless power transmittingapparatus.

Yet another embodiment of the present invention relates to a wirelesspower receiving apparatus configured to receive an electric power signalcomprising any one from among an electric field, a magnetic field, andan electromagnetic field, transmitted from a wireless power transmittingapparatus. The wireless power receiving apparatus comprises: a receptionantenna comprising a reception coil; and an automatic tuning assistcircuit coupled with the reception antenna. The automatic tuning assistcircuit comprises: a first terminal; a second terminal; N (N representsan integer) auxiliary capacitors; multiple switches; and a secondcontrol unit. Each of the multiple switches is arranged between twoterminals from among the first terminal, the second terminal, and theterminals of the N auxiliary capacitors. The second control unit isconfigured to switch on and off the multiple switches.

When the frequency of the electric power signal does not match theresonance frequency of the resonance circuit including the receptionantenna, the resonance circuit functions as a capacitor circuit orotherwise an inductor circuit. In this case, a resonance current flowsthrough the resonance circuit with a phase that is delayed or otherwiseadvanced with respect to the phase of resonance voltage that is inducedin the resonance circuit. In this state, in a case in which the thirdswitch and the fourth switch are switched on and off with the samefrequency as that of the electric power signal, the third auxiliarycapacitor is charged or otherwise discharged so as to provide phasematching between the resonance current and the resonance voltage. Byapplying the correction voltage that develops at the third auxiliarycapacitor to the reception antenna, such an arrangement provides aquasi-resonant state. Such an embodiment is capable of automaticallytuning the reception antenna with respect to the electric power signaleven without an operation such as adjusting the capacitance of theresonance capacitor.

Also, the second control unit may be configured to switch on and offeach of the multiple switches with the same frequency as that of theelectric power signal, or otherwise with a frequency obtained bymultiplying or dividing the frequency of the electric power signal by anodd number.

Also, the automatic tuning assist circuit may comprise: a third switchand a third auxiliary capacitor arranged in series between the firstterminal and the second terminal; and a fourth switch arranged betweenthe first terminal and the second terminal such that it is arranged inparallel with the third switch and the third auxiliary capacitor.

Also, the second control unit may be configured to switch on and off thethird switch and the fourth switch with the same frequency as that ofthe electric power signal.

Also, the second control unit may be configured to drive the thirdswitch and the fourth switch with a predetermined phase difference withrespect to the driving voltage applied to the transmission antenna ofthe wireless power transmitting apparatus.

Also, with an embodiment, the automatic tuning assist circuit mayfurther comprise a fourth auxiliary capacitor between the first terminaland the second terminal such that it is arranged in series with thefourth switch.

With such an arrangement, the fourth auxiliary capacitor is charged orotherwise discharged so as to provide phase matching between theresonance current and the driving voltage, in addition to charging orotherwise discharging the third auxiliary capacitor. Such an arrangementis capable of providing a quasi-resonant state.

Also, the third switch and the fourth switch may each be configured as auni-directional switch. Also, the second control unit may be configuredto switch on and off the third switch and the fourth switch with a phasecontrolled such that no current flows through each of their inverselyconducting elements.

Also, the third switch and the fourth switch may each be configured as abi-directional switch. Such an arrangement is capable of relaxing thephase constraints on the switching operation.

Also, a load to be supplied with electric power may be connected to thethird auxiliary capacitor. Also, a load to be supplied with electricpower may be connected to a first end of the reception antenna.

Also, the wireless power receiving apparatus according to an embodimentmay further comprise a transformer having a primary winding connected inseries with the reception antenna. Also, a load to be supplied withelectric power may be connected to a secondary winding of thetransformer.

Also, the automatic tuning assist circuit may be coupled in series withthe reception antenna via a transformer.

Also, the reception antenna may comprise a resonance capacitor arrangedin series with the reception coil.

Yet another embodiment of the present invention relates to a wirelesspower supply system. The wireless power supply system comprises: awireless power transmitting apparatus configured to transmit an electricpower signal comprising any one from among an electric field, a magneticfield, and an electromagnetic field; and a wireless power receivingapparatus according to any one of the aforementioned embodiments,configured to receive the electric power signal.

Yet another embodiment of the present invention relates to an automatictuning assist circuit employed in a wireless power transmittingapparatus, and coupled with the transmission coil. The automatic tuningassist circuit comprises: at least one auxiliary capacitor; multipleswitches arranged in order to charge and discharge the respectiveaforementioned at least one auxiliary capacitor using a resonancecurrent that flows through the transmission coil; and a first controlunit configured to switch on and off the multiple switches so as togenerate a capacitor voltage across the respective aforementioned atleast one auxiliary capacitor, and to apply, to the transmission coil, acorrection voltage that corresponds to the capacitor voltage thatdevelops at the aforementioned at least one auxiliary capacitor.

By providing such an automatic tuning assist circuit, such anarrangement provides a quasi-resonant state. Thus, such an arrangementis capable of automatically tuning the transmission antenna with respectto the driving voltage even without an operation such as adjusting thecapacitance of the resonance capacitor.

Yet another embodiment of the present invention relates to an automatictuning assist circuit employed in a wireless power receiving apparatus,and coupled with the reception coil. The automatic tuning assist circuitcomprises: at least one auxiliary capacitor; multiple switches arrangedin order to charge and discharge the respective aforementioned at leastone auxiliary capacitor using a resonance current that flows through thereception coil; and a second control unit configured to switch on andoff the multiple switches so as to generate a capacitor voltage acrossthe respective aforementioned at least one auxiliary capacitor, and toapply, to the reception coil, a correction voltage that corresponds tothe capacitor voltage that develops at the aforementioned at least oneauxiliary capacitor.

By providing such an automatic tuning assist circuit, such anarrangement provides a quasi-resonant state. Thus, such an arrangementis capable of automatically tuning the reception antenna with respect tothe electric power signal even without an operation such as adjustingthe capacitance of the resonance capacitor.

It is to be noted that any arbitrary combination or rearrangement of theabove-described structural components and so forth is effective as andencompassed by the present embodiments.

Moreover, this summary of the invention does not necessarily describeall necessary features so that the invention may also be asub-combination of these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a diagram showing a wireless power transmission systemaccording to a comparison technique;

FIG. 2 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus according to a first embodiment;

FIGS. 3A through 3F are diagrams each showing an example configurationof a switch employing MOSFETs;

FIG. 4 is a waveform diagram showing the operation of the wireless powertransmitting apparatus shown in FIG. 2;

FIG. 5 is an equivalent circuit diagram of the wireless powertransmitting apparatus shown in FIG. 2;

FIG. 6A is a waveform diagram showing a state in which an automatictuning assist circuit does not operate, and FIG. 6B is a waveformdiagram showing a state in which the automatic tuning assist circuitoperates;

FIG. 7 is a phasor diagram for describing a quasi-resonant stateprovided by the automatic tuning assist circuit in a case in whichf_(c)<f_(TX);

FIG. 8 is a diagram showing a resonance current in a non-resonant stateand in a resonance state;

FIG. 9 is a phasor diagram for describing a quasi-resonant stateprovided by the automatic tuning assist circuit in a case in whichf_(c)>f_(TX);

FIG. 10 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus according to a first modification;

FIG. 11 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus according to a second modification;

FIG. 12 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus according to a third modification;

FIGS. 13A and 13B are circuit diagrams showing the configurations ofwireless power transmitting apparatuses according to a fourthmodification and a fifth modification, respectively;

FIG. 14 is a circuit diagram showing a configuration of a wireless powerreceiving apparatus according to the first embodiment;

FIG. 15 is an equivalent circuit diagram of the wireless powertransmitting apparatus shown in FIG. 14;

FIG. 16 is a waveform diagram showing the operation of the wirelesspower receiving apparatus shown in FIG. 14;

FIGS. 17A and 17B are circuit diagrams showing the configurations ofwireless power receiving apparatuses according to a first modificationand a second modification;

FIG. 18 is a circuit diagram showing a configuration of a wireless powerreceiving apparatus according to a third modification;

FIGS. 19A and 19B are circuit diagrams showing the configurations ofwireless power receiving apparatuses according to a fourth modificationand a fifth modification, respectively;

FIG. 20 is a circuit diagram showing an example configuration of awireless power transmission system according to the first embodiment;

FIG. 21 is a waveform diagram showing the operation of the wirelesspower transmission system shown in FIG. 20;

FIG. 22 is a circuit diagram showing a configuration of a wireless powerreceiving apparatus according to a second embodiment;

FIG. 23 is a waveform diagram showing the operation of the wirelesspower transmitting apparatus shown in FIG. 22;

FIG. 24 is a circuit diagram showing the configuration of a wirelesspower transmitting apparatus according to a first modification;

FIGS. 25A through 25C are circuit diagrams showing the configurations ofwireless power transmitting apparatuses according to a secondmodification through a fourth modification, respectively;

FIG. 26 is a circuit diagram showing a configuration of a wireless powerreceiving apparatus according to the second embodiment;

FIG. 27 is a waveform diagram showing the operation of the wirelesspower receiving apparatus shown in FIG. 26;

FIGS. 28A and 28B are circuit diagrams showing the configurations ofwireless power receiving apparatuses according to a second modificationand a third modification, and FIGS. 28C and 28D are circuit diagramseach showing an example configuration of a load; and

FIG. 29 is a circuit diagram showing a configuration of a wireless powerreceiving apparatus according to a third modification.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on preferred embodiments whichdo not intend to limit the scope of the present invention but exemplifythe invention. All of the features and the combinations thereofdescribed in the embodiment are not necessarily essential to theinvention.

In the present specification, the state represented by the phrase “themember A is connected to the member B” includes a state in which themember A is indirectly connected to the member B via another member thatdoes not substantially affect the electric connection therebetween, orthat does not damage the functions or effects of the connectiontherebetween, in addition to a state in which the member A is physicallyand directly connected to the member B.

Similarly, the state represented by the phrase “the member C is providedbetween the member A and the member B” includes a state in which themember A is indirectly connected to the member C, or the member B isindirectly connected to the member C via another member that does notsubstantially affect the electric connection therebetween, or that doesnot damage the functions or effects of the connection therebetween, inaddition to a state in which the member A is directly connected to themember C, or the member B is directly connected to the member C.

[First Embodiment]

[Wireless Power Transmitting Apparatus]

FIG. 2 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus 2 according to a first embodiment. The wirelesspower transmitting apparatus 2 is configured to transmit an electricpower signal S1 to a wireless power receiving apparatus (not shown). Assuch an electric power signal S1, the wireless power transmittingapparatus 2 uses the near-field components (electric field, magneticfield, or electromagnetic field) of electromagnetic waves that have notyet become radio waves.

The wireless power transmitting apparatus 2 includes a power supply 10,a transmission antenna 20, an automatic tuning assist circuit 30, and afirst control unit 40.

The transmission antenna 20 includes a transmission coil L_(TX) arrangedbetween its first terminal 21 and its second terminal 22. A resonancecapacitor C_(TX) is arranged in series with the transmission coilL_(TX). The resonance capacitor C_(TX) and the transmission coil L_(TX)may also be mutually exchanged.

The automatic tuning assist circuit 30 is coupled in series with thetransmission antenna 20. The power supply 10 is configured to apply anAC driving voltage V_(DRV) having a predetermined transmission frequencyf_(TX) between the respective terminals of a circuit comprising thetransmission antenna 20 and the automatic tuning assist circuit 30. Thedriving voltage V_(DRV) may be configured to have a desired AC waveform,examples of which include a rectangular waveform, a trapezoidalwaveform, a sine waveform, and the like. With the present embodiment,the driving voltage V_(DRV) is configured as a rectangular wave signalwhich swings between a first voltage level (power supply voltage V_(DD))and a second voltage level (ground voltage V_(GND)=0 V).

The power supply 10 includes a DC power supply 12, a first high-sideswitch SWH1, and a first low-side switch SWL1. The DC power supply 12 isconfigured to generate a DC power supply voltage V_(DD). The firsthigh-side switch SWH1 and the first low-side switch SWL1 aresequentially connected in series between the output terminal of the DCpower supply 12 and a fixed voltage terminal (ground terminal). Thefirst control unit 40 is configured to switch on and off the firsthigh-side switch SWH1 and the first low-side switch SWL1 in acomplementary manner, with a transmission frequency f_(TX).

The automatic tuning assist circuit 30 includes a first terminal 31, asecond terminal 32, a first switch SW1, a second switch SW2, and a firstauxiliary capacitor C_(A1).

The first switch SW1 and the first auxiliary capacitor C_(A1) arearranged in series between the first terminal 31 and the second terminal32. The first switch SW1 and the first auxiliary capacitor C_(A1) mayalso be mutually exchanged. The second switch SW2 is arranged inparallel with the first switch SW1 and the first auxiliary capacitorC_(A1) between the first terminal 31 and the second terminal 32. Thefirst auxiliary capacitor C_(A1) is preferably configured to have asufficiently greater capacitance than that of the resonance capacitorC_(TX).

The first control unit 40 is configured to switch on and off the firstswitch SW1 and the second switch SW2 in a complementary manner, with thesame frequency f_(TX) as that of the driving voltage V_(DRV), and with apredetermined phase difference θ_(TX) with respect to the drivingvoltage V_(DRV). The phase difference θ_(TX) may preferably be set to avalue in the vicinity of +90 degrees or otherwise −90 degrees (270degrees). That is to say, a part of the first control unit 40 functionsas a component of the automatic tuning assist circuit 30.

The first switch SW1 and the second switch SW2 are each configuredemploying a MOSFET (Metal Oxide Semiconductor Field Effect Transistor),IGBT (Insulated Gate Bipolar Transistor), bipolar transistor, or thelike. FIGS. 3A and 3B are diagrams each showing an example configurationof a switch employing a MOSFET.

FIG. 3A shows a configuration of the switch employing an N-channelMOSFET. FIG. 3B shows a configuration of the switch employing aP-channel MOSFET. In a case in which the back gate of the MOSFET isconnected to its source, the body diode that forms between the back gateand the drain is in the connection state regardless of the gate voltage.Thus, such a switch configured as a single MOSFET is not capable ofblocking a current that flows in one particular direction. In thepresent specification, such a switch will be referred to as a“uni-directional switch”.

The switches shown in FIGS. 3C through 3F each comprise two N-channelMOSFETs or otherwise two P-channel MOSFETs connected such that theirbody diodes are connected in reverse directions (back-to-backconnection). With the switches shown in FIGS. 3C through 3F, in the offstate, no current flows in either direction. In the presentspecification, such a switch will be referred to as a “bi-directionalswitch”.

With the present embodiment, the switches SW1 and SW2 may each beconfigured as a uni-directional switch or otherwise a bi-directionalswitch. It should be noted that, in a case in which the switches SW1 andSW2 are each configured as a uni-directional switch, there is a need topay attention to their switching phases. Detailed description thereofwill be made later.

The above is the configuration of the wireless power transmittingapparatus 2. Next, description will be made regarding the operationthereof.

Let us consider an arrangement in which the switches SW1 and SW2 areeach configured as a bi-directional switch which is capable of blockinga current in both directions in the off state.

FIG. 4 shows waveform diagrams each showing the operation of thewireless power transmitting apparatus 2 shown in FIG. 2. FIG. 4 shows,in the following order beginning from the top, the voltage at the firsthigh-side switch SWH1, the voltage at the first low-side switch SWL1,the driving voltage V_(DRV), the voltage at the first switch SW1, thevoltage at the second switch SW2, the voltage V_(CA1) at the firstauxiliary capacitor C_(A1), the voltage V_(A) at the first terminal 31,the resonance current I_(TX) that flows through the transmission antenna20, and the resonance voltage V_(TX) that develops across thetransmission coil L_(TX) and the resonance capacitor C_(TX). In thewaveform diagram for each switch, the high level represents the onstate, and the low level represents the off state. It should be notedthat FIG. 4 shows the waveforms of the resonance current I_(TX) and theresonance voltage V_(TX) obtained after a sufficient time has elapsedafter the automatic tuning assist circuit 30 starts to operate.

As shown in FIG. 4, by switching on and off the first high-side switchSWH1 and the first low-side switch SWL1 in a complementary manner, suchan arrangement is capable of generating the driving voltage V_(DRV)having a rectangular waveform. The driving voltage V_(DRV) thusgenerated is applied across the transmission antenna 20 and theautomatic tuning assist circuit 30. The first control unit 40 isconfigured to switch on and off the first switch SW1 and the secondswitch SW2 in a complementary manner, with the same frequency as that ofthe driving voltage V_(DRV), and with a phase that is delayed by θ_(TX)(=90 degrees) with respect to the driving voltage V_(DRV). The resonancecurrent I_(TX) flows to the first auxiliary capacitor C_(A1) during theon time T_(ON1) of the first switch SW1, and flows to the ground via thesecond switch SW2 during the on time T_(ON2) of the second switch SW2.That is to say, the first auxiliary capacitor C_(A1) is charged anddischarged by means of the resonance current I_(TX). As a result, thecapacitor voltage V_(CA1) develops at the first auxiliary capacitorC_(A1).

The automatic tuning assist circuit 30 is configured to apply acorrection voltage V_(A) to the second terminal 22 of the transmissionantenna 20. During the on time T_(ON1) of the first switch SW1, thefirst auxiliary capacitor voltage V_(CA1) is used as the correctionvoltage V_(A). On the other hand, during the on time T_(ON2) of thesecond switch SW2, the ground voltage V_(GND) is used as the correctionvoltage V_(A). The automatic tuning assist circuit 30 can be regarded asa correction power supply configured to apply the correction voltageV_(A) to the transmission antenna 20. FIG. 5 is an equivalent circuitdiagram showing an equivalent circuit of the wireless power transmittingapparatus 2 shown in FIG. 2.

FIG. 6A is a waveform diagram showing a state in which the automatictuning assist circuit 30 does not operate, and FIG. 6B is a waveformdiagram showing a state in which the automatic tuning assist circuit 30operates.

First, description will be made with reference to FIG. 6A regarding thestate in which the automatic tuning assist circuit 30 does not operate,i.e., a state in which the first switch SW1 is fixed to the off state,and the second switch SW2 is fixed to the on state. In this state, thecorrection voltage V_(A) is fixed to the ground voltage V_(GND).

The impedance Z of the transmission antenna 20 is represented by thefollowing Expression (1). The resonance frequency f_(c) of thetransmission antenna 20 is represented by the following Expression (2).The following Expressions (1) and (2) represent the impedance and theresonance frequency assuming that the resistance component isnegligible. However, it is needless to say that, in actual circuits, theresistance component connected in series contributes to the circuitimpedance.Z=jωL _(TX)+1/(jωC _(TX))  (1)f _(c)=1/2π√(L _(TX) ·C _(TX))  (2)

In a case in which the frequency f_(TX) of the driving voltage V_(DRV)is higher than the resonance frequency f_(c) (f_(TX)>f_(c)), thetransmission antenna 20 functions as an inductor. In this case, theresonance current I_(TX) that flows through the transmission antenna 20has a phase which is delayed with respect to the phase of the drivingvoltage V_(DRV). Conversely, in a case in which the frequency f_(TX) ofthe driving voltage V_(DRV) is lower than the resonance frequency f_(c)(f_(TX)<f_(c)), the transmission antenna 20 functions as a capacitor. Inthis case, the resonance current I_(TX) has a phase which is advancedwith respect to the driving voltage V_(DRV).

FIG. 6A shows a state in which f_(c)>f_(TX). In this state, theresonance current I_(TX) has a phase which is advanced by the phasedifference ϕ with respect to the driving voltage V_(DRV). It should benoted that the phase difference ϕ is not 90 degrees. This is because theresonance circuit includes a non-negligible resistance component (notshown) connected in series. In the non-resonant state, the impedance Zexhibits a high value, leading to a reduced amplitude of the resonancecurrent I_(TX). In this state, such an arrangement is not capable oftransmitting a large amount of electric power.

Next, description will be made with reference to FIG. 6B regarding acase in which the automatic tuning assist circuit 30 operates.

In a case in which the automatic tuning assist circuit 30 operates, thecorrection voltage V_(A) is applied to the transmission antenna 20 witha phase that is delayed by θ_(TX)=90 degrees with respect to the drivingvoltage V_(DRV). As a result, phase matching is obtained between theresonance current I_(TX) and the driving voltage V_(DRV), therebyproviding a quasi-resonant state. In this state, the resonance currentI_(TX) has a greater amplitude than that in the non-resonant state.

FIG. 7 is a phasor diagram (vector diagram) for describing thequasi-resonant state provided by the automatic tuning assist circuit 30.

The phase of the driving voltage V_(DRV) is 0 degrees. The phase of thecorrection voltage V_(A) is θ_(TX)=90 degrees. In a case in whichf_(c)<f_(TX), the current has a phase that is delayed by the phasedifference ϕ with respect to the voltage. Thus, the phase difference ϕexists between the driving voltage V_(DRV) and the current componentI_(DRV). Furthermore, the phase difference ϕ exists between thecorrection voltage V_(A) and the current component V_(A).

Based on the “principle of superposition”, the resonance current I_(TX)is configured as the sum of the current component I_(DRV) induced by thedriving voltage V_(DRV) and the current component I_(A) induced by thecorrection voltage V_(A). There is a phase difference of θ_(TX) (=90degrees) between the driving voltage V_(DRV) and the correction voltageV_(A). Accordingly, there is a phase difference of 90 degrees betweenthe current components I_(DRV) and I_(A). Thus, by optimizing theamplitude of the correction voltage V_(A), i.e., by optimizing theamplitude of the current component I_(A), such an arrangement is capableof providing phase matching between the driving voltage V_(DRV) (havinga phase of 0 degrees) and a resultant current obtained by combining thetwo current components I_(DRV) and I_(A), i.e., the resonance currentI_(TX). That is to say, it can be clearly understood that such anarrangement provides a quasi-resonant state.

The wireless power transmitting apparatus 2 according to the embodimentis capable of automatically generating the correction voltage V_(A)which provides the quasi-resonant state, which is an important excellentadvantage of the wireless power transmitting apparatus 2 according tothe embodiment.

FIG. 8 is a diagram showing the resonance current I_(TX) in thenon-resonant state and in the resonance state. The waveform (I)represents the resonance current I_(TX) in the non-resonant state. Inthe on time T_(ON1) in which the switch SW1 is on, the first auxiliarycapacitor C_(A1) is charged and discharged by means of the resonancecurrent I_(TX). Specifically, the first auxiliary capacitor C_(A1) ischarged during a period in which the resonance current I_(TX) ispositive, and is discharged during a period in which the resonancecurrent I_(TX) is negative. As a result, in a case in which the periodin which the resonance current I_(TX) is positive is longer than theperiod in which the resonance current I_(TX) is negative, the capacitorvoltage V_(CA1) rises. Otherwise, the capacitor voltage V_(CA1) drops.

Let us say that the capacitor voltage V_(CA1) rises in the on timeT_(ON1) of a certain cycle. In this case, the correction voltage V_(A)is applied to the transmission antenna 20 according to the risingcapacitor voltage V_(CA1). This advances the phase of the resonancecurrent I_(TX) with respect to the resonance current I_(TX) of theprevious cycle. By repeatedly performing this processing, the capacitorvoltage V_(CA1) rises in increments of cycles, which gradually advancesthe phase of the resonance current I_(TX). Eventually, the phase of theresonance current I_(TX) shifts until it matches the phase of thedriving voltage V_(DRV) (resonance point). When the phase of theresonance current I_(TX) exceeds the resonance point, the dischargecurrent of the first auxiliary capacitor C_(A1) becomes greater than itscharging current, thereby providing a feedback control operation in thereverse direction. This reduces the capacitor voltage V_(CA1), therebyreturning the phase of the resonance current I_(TX) to the resonancepoint. At the resonance point, such an arrangement provides a balancebetween the charging current and the discharging current of the firstauxiliary capacitor C_(A1) for each cycle, thereby providing anequilibrium state of the capacitor voltage V_(CA1). In this state, aquasi-resonant state is maintained. As described above, with thewireless power transmitting apparatus 2 shown in FIG. 2, such anarrangement is capable of automatically generating the correctionvoltage V_(A) that is required to provide the quasi-resonant state.

The above is the operation of the wireless power transmitting apparatus2.

As described above, without adjusting the resonance frequency f_(c) ofthe transmission antenna 20, the wireless power transmitting apparatus 2is capable of automatically tuning the circuit state so as to providethe quasi-resonant state. In the wireless power transmission, theresonance frequency changes over time according to the position relationbetween the wireless power transmitting apparatus 2 and the wirelesspower receiving apparatus 4. The wireless power transmitting apparatus 2is capable of following the change in the resonance frequency with highspeed, thereby providing high-efficiency electric power transmission.

Furthermore, in a case in which a large amount of electric power istransmitted by means of wireless power transmission, a very high voltagedevelops between both ends of the resonance capacitor C_(TX), whichlimits the use of a variable capacitor. With the wireless powertransmitting apparatus 2, there is no need to adjust the capacitance ofthe resonance capacitor C_(TX). Thus, such an arrangement does notrequire such a variable capacitor or the like, which is anotheradvantage.

Description has been made above regarding a case in which the firstswitch SW1 is switched on and off with a phase that is delayed by θ_(TX)(=90 degrees) with respect to the phase of the switching of the firsthigh-side switch SWH1. However, the phase difference θ_(TX) between thefirst switch SW1 and the first high-side switch SWH1 is not restrictedto 90 degrees. Also, an arrangement may be made in which the phasedifference θ_(TX) between the first switch SW1 and the first high-sideswitch SWH1 is set to 270 degrees (−90 degrees). In this case, thecapacitor voltage V_(CA1) is automatically adjusted such that it becomesa negative voltage.

That is to say, in a case in which f_(c)<f_(TX), by setting the phasedifference θ_(TX) to 90 degrees or otherwise 270 degrees, such anarrangement provides a quasi-resonant state.

Also, the phase difference θ_(TX) may be moved away from 90 degrees or270 degrees. In this case, the phase difference θ_(TX) between thecurrent components I_(DRV) and I_(A) does not match 90 degrees. However,even in such a case, the capacitor voltage V_(CA1) is automaticallyadjusted such that the resultant resonance current I_(TX) has a phase of0 degrees. It should be noted that, as the phase difference θ_(TX)becomes closer to 90 degrees or otherwise 270 degrees, the requiredvalue of the amplitude of the current component I_(A), i.e., therequired absolute value of the capacitor voltage V_(CA1), becomessmaller. This is an advantage in employing an arrangement in which thephase difference θ_(TX) is set to 90 degrees or otherwise 270 degrees.

It should be noted that, in a case in which f_(c)<f_(TX), such anarrangement is capable of supporting the quasi-resonant state in whichthe phase difference θ_(TX) is set to 270 degrees only in a case inwhich the first switch SW1 and the second switch SW2 are each configuredas a bi-directional switch. In other words, in a case in which the firstswitch SW1 and the second switch SW2 are each configured as auni-directional switch, such an arrangement is not capable of supportingthe quasi-resonant state in which the phase difference θ_(TX) is set to270 degrees. This is because the current flows through the body diode.Thus, in a case in which the first switch SW1 and the second switch SW2are each configured as a uni-directional switch, there is a need toswitch on and off the first switch SW1 and the second switch SW2 with aphase such that no current flows through the body diodes which eachfunction as an inversely conducting element.

The wireless power transmitting apparatus 2 automatically provides aquasi-resonant state not only in a case in which f_(c)<f_(TX), but alsoin a case in which f_(c)>f_(TX). In this case, the phase differenceθ_(TX) is preferably set to 270 degrees (−90 degrees).

FIG. 9 is a phasor diagram for describing a quasi-resonant stateprovided by the automatic tuning assist circuit 30 in a case in whichf_(c)>f_(TX). Description will be made below assuming that the drivingvoltage V_(DRV) has a phase of 0 degrees, and the correction voltageV_(A) has a phase θ_(TX) of 270 degrees (−90 degrees). In a case inwhich f_(c)>f_(TX), the current has a phase which is advanced withrespect to that of the voltage. Such an arrangement also provides aquasi-resonant state even in such a case.

It should be noted that, in a case in which f_(c)>f_(TX), the phasedifference θ_(TX) may be set to a value in the vicinity of 90 degrees.In this case, the capacitor voltage V_(CA1) is automatically adjustedsuch that it becomes a negative voltage so as to provide aquasi-resonant state.

It should be noted that, in a case in which f_(c)<f_(TX), such anarrangement is capable of supporting the quasi-resonant state in whichthe phase difference θ_(TX) is set to 90 degrees only in a case in whichthe first switch SW1 and the second switch SW2 are each configured as abi-directional switch. In other words, in a case in which the firstswitch SW1 and the second switch SW2 are each configured as auni-directional switch, such an arrangement is not capable of supportingthe quasi-resonant state in which the phase difference θ_(TX) is set to90 degrees. This is because the current flows through the body diode.

Next, description will be made regarding modifications of the wirelesspower transmitting apparatus 2. Each modification may be combined withany one of the other modifications, which is encompassed within thescope of the present invention.

Description has been made above regarding an arrangement in which thefirst control unit 40 drives multiple switches included in the automatictuning assist circuit 30 with the same frequency f_(TX) as that of thedriving voltage V_(DRV). However, the present invention is notrestricted to such an arrangement. Also, the first control unit 40 maybe configured to switch on and off the aforementioned switches with afrequency obtained by multiplying or dividing the frequency of thedriving voltage V_(DRV) by an odd number. Such an arrangement alsoprovides a quasi-resonant state.

FIG. 10 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus 2 a according to a first modification. Anautomatic tuning assist circuit 30 a includes a second auxiliarycapacitor C_(A2) between the first terminal 31 and the second terminal32 such that it is connected in series with the second switch SW2.

With such a modification, during the on time T_(ON1) of the first switchSW1, the correction voltage V_(A) is set to the capacitor voltageV_(CA1). During the on time T_(ON2) of the second switch SW2, thecorrection voltage V_(A) is set to the capacitor voltage V_(CA2).

With the wireless power transmitting apparatus 2 a, by optimizing thecapacitor voltages V_(CA1) and V_(CA2), such an arrangement provides aquasi-resonant state both in the case in which V_(TX)>f_(c) and in thecase in which V_(TX)<f_(c).

FIG. 11 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus 2 b according to a second modification. Anautomatic tuning assist circuit 30 b includes a charger circuit 34 and adetection resistor Rs. The detection resistor Rs is arranged on a pathof the resonance current I_(TX). A detection voltage V_(S) develops atthe detection resistor Rs in proportion to the resonance current I_(TX).The charger circuit 34 is configured to charge the first auxiliarycapacitor C_(A1) based on the detection voltage V_(S) so as to provide aquasi-resonant state. As described above, the capacitor voltage V_(CA1)automatically becomes the optimum level. In addition, by providing thecharger circuit 34, such an arrangement provides a quasi-resonant statein a shorter period of time.

FIG. 12 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus 2 c according to a third modification.Description has been made in which the power supply is configured as ahalf-bridge circuit. In contrast, a power supply 10 c shown in FIG. 12is configured as an H-bridge circuit. A second high-side switch SWH2 anda second low-side switch SWL2 are sequentially connected in seriesbetween the output terminal of the power supply 12 and a fixed voltageterminal (ground terminal).

The first control unit 40 c is configured to repeatedly switch statesbetween a state in which the pair of the high-side switch SWH1 and thesecond low-side switch SWL2 are turned on and a state in which the pairof the second high-side switch SWH2 and the first low-side switch SWL1are turned on.

A driving voltage V_(DRV) that develop at a connection node (firstoutput terminal) OUT1 that connects the first high-side switch SWH1 andthe first low-side switch SWL1 has a phase that is the reverse of thephase of a driving voltage #V_(DRV) that develops at a connection node(second output terminal) OUT2 that connects the second high-side switchSWH2 and the second low-side switch SWL2. The transmission antenna 20and an automatic tuning assist circuit 30 c are coupled in seriesbetween the first output terminal OUT1 and the second output terminalOUT2.

With the wireless power transmitting apparatus 2 c shown in FIG. 12,such an arrangement provides the same advantages as those provided bythe wireless power transmitting apparatus described above.

FIGS. 13A and 13B are circuit diagrams showing the configurations ofwireless power transmitting apparatuses 2 d and 2 e according to afourth modification and a fifth modification. The first control unit 40is omitted from the diagrams.

With the wireless power transmitting apparatus 2 d shown in FIG. 13A, anautomatic tuning assist circuit 30 d is coupled in series with thetransmission antenna 20 via a first transformer T1. Specifically, asecondary winding W2 of the first transformer T1 is arranged between thefirst terminal 31 and the second terminal 32, and a primary winding W1of the first transformer T1 is arranged in series with the transmissionantenna 20. The power supply 10 is configured to apply a driving voltageacross the transmission antenna 20 and the primary winding W1.

With the wireless power transmitting apparatus 2 d, energy istransmitted and received between the transmission antenna 20 and theautomatic tuning assist circuit 30 d via the transformer T1. Such anarrangement provides the same advantages as those provided by thewireless power transmitting apparatuses described above.

With an arrangement shown in FIG. 13B, the power supply 10 is configuredto apply the driving voltage V_(DRV) across the transmission antenna 20and the automatic tuning assist circuit 30 d via the second transformerT2. Specifically, the secondary winding W2 of the second transformer T2is arranged in series with the transmission antenna 20. The power supply10 is configured to apply the driving voltage V_(DRV) between both endsof the primary winding W1 of the second transformer T2.

With the wireless power transmitting apparatus 2 e, the driving voltageV_(DRV) is applied across the transmission antenna 20 and the automatictuning assist circuit 30 d via the second transformer T2. Such anarrangement also provides the same advantages as those of the wirelesspower transmitting apparatuses described above. With the wireless powertransmitting apparatus 2 e, the first transformer T1 may be omitted. Thepower supply 10 shown in FIGS. 13A and 13B may be configured as anH-bridge circuit, a half-bridge circuit, or any other kind of powersupply.

[Wireless Power Receiving Apparatus]

The automatic tuning assist circuit described above may also be employedin the wireless power receiving apparatus. Description will be madebelow regarding such a wireless power receiving apparatus.

FIG. 14 is a circuit diagram showing a configuration of a wireless powerreceiving apparatus 4 according to the first embodiment. The wirelesspower receiving apparatus 4 is configured to receive the electric powersignal S1 transmitted from the aforementioned wireless powertransmitting apparatus or otherwise a wireless power transmittingapparatus having an entirely different configuration. The electric powersignal S1 is configured using the near-field components (electric field,magnetic field, or electromagnetic field) of electromagnetic waves thathave not yet become radio waves.

The wireless power receiving apparatus 4 includes a reception antenna50, an automatic tuning assist circuit 60, and a load 70 to be suppliedwith electric power. The load 70 may include an unshown rectifiercircuit, detector circuit, or the like, as a built-in component.

The reception antenna 50 includes a reception coil L_(RX) and aresonance capacitor C_(RX) arranged in series between a first terminal51 and a second terminal 52.

The automatic tuning assist circuit 60 has the same configuration asthat of the automatic tuning assist circuit 30 described above.Specifically, a third switch SW3 and a third auxiliary capacitor C_(A3)are arranged between a first terminal 61 and a second terminal 62.Furthermore, a fourth switch SW4 is arranged between the first terminal61 and the second terminal 62 such that it is connected in parallel withthe third switch SW3 and the third auxiliary capacitor C_(A3).

The second control unit 64 is configured to switch on and off the thirdswitch SW3 and the fourth switch SW4 in a complementary manner, with thesame frequency as that of the electric power signal S1 and with a phasedifference θ_(RX) with respect to the driving voltage (V_(DRV)) which isapplied to the transmitter-side antenna. For example, the phasedifference θ_(RX) is set to 180 degrees or otherwise 0 degrees.

The automatic tuning assist circuit 60 is coupled in series with thereception antenna 50. Furthermore, the load 70 to be supplied withelectric power is connected to the third auxiliary capacitor C_(A3).

The above is the configuration of the wireless power receiving apparatus4. Next, description will be made regarding the operation thereof. FIG.15 is an equivalent circuit diagram showing an equivalent circuitconfiguration of the wireless power receiving apparatus 4 shown in FIG.14. As with the automatic tuning assist circuit 30 of the wireless powertransmitting apparatus 2, the automatic tuning assist circuit 60 can beregarded as a correction power supply configured to apply a correctionvoltage V_(A) to the reception antenna 50. During the on time T_(ON3) inwhich the third switch SW3 is turned on, the correction voltage V_(A) isset to the voltage V_(CA3) that develops at the third auxiliarycapacitor C_(A3). During the on time T_(ON4) of the fourth switch SW4,the correction voltage V_(A) is set to the ground voltage.

FIG. 16 is a waveform diagram showing the operation of the wirelesspower receiving apparatus 4 shown in FIG. 14. FIG. 16 shows, in thefollowing order beginning from the top, the voltages applied to thethird switch SW3 and the fourth switch SW4, the correction voltageV_(A), the resonance current I_(RX) that flows through the receptionantenna 50, and the resonance voltage V_(RX) that develops across thereception coil L_(RX) and the resonance capacitor C_(RX). In thewaveform diagrams showing the voltages applied to the respectiveswitches, the high-level state represents the on state, and thelow-level state represents the off state. In the waveform diagramsshowing the resonance current I_(RX) and the resonance voltage V_(RX),the solid line represents the waveform of a steady state (quasi-resonantstate) after a sufficient period of time elapses after the automatictuning assist circuit 60 starts to operate, and the broken linerepresents the waveform of a non-resonant state when the automatictuning assist circuit 60 does not operate.

By switching on and off the third switch SW3 and the fourth switch SW4in a complementary manner, with a phase θ_(RX) which is shifted by 180degrees or otherwise 0 degrees with respect to the driving voltageV_(DRV) of the wireless power transmitting apparatus side, such anarrangement charges or otherwise discharges the third auxiliarycapacitor C_(A3). Furthermore, by applying the correction voltage V_(A)to the reception antenna 50, such an arrangement allows the resonancecurrent I_(A) to have a phase matching the phase of the driving voltageV_(DRV) of the transmission side, thereby providing a quasi-resonantstate.

In order to provide a quasi-resonant state, there is a need to switch onand off the third switch SW3 and the fourth switch SW4 with a suitablefrequency f_(TX) and with a suitable phase θ_(RX). In order to meet thisrequirement, the wireless power transmitting apparatus 2 may beconfigured to transmit the data which represents the frequency f_(TX)and the phase θ_(RX) to the wireless power receiving apparatus 4. Also,the wireless power receiving apparatus 4 may be configured to sweep thephase θ_(RX) so as to detect the optimum phase θ_(RX).

The above is the operation of the wireless power receiving apparatus 4.

As described above, with the wireless power receiving apparatus 4 shownin FIG. 14, such an arrangement automatically provides a resonant statewithout a need to adjust the capacitance of the resonance capacitorC_(RX).

Next, description will be made regarding modifications of the wirelesspower receiving apparatus 4.

Description has been made above regarding an arrangement in which thesecond control unit 64 drives the multiple switches, which arecomponents of the automatic tuning assist circuit 60, with the samefrequency as that of the electric power signal S1. However, the presentinvention is not restricted to such an arrangement. Also, the secondcontrol unit 64 may be configured to switch on and off theaforementioned switches with a frequency obtained by multiplying ordividing the frequency of the electric power signal S1 by an odd number.Such an arrangement also provides a quasi-resonant state.

Description has been made with reference to FIG. 14 regarding anarrangement in which the load 70 is connected to the third auxiliarycapacitor C_(A3). Also, the load 70 may be connected to a differentposition. FIGS. 17A and 17B are circuit diagrams showing theconfigurations of wireless power receiving apparatuses according to afirst modification and a second modification. With a wireless powerreceiving apparatus 4 a shown in FIG. 17A, a load 70 a is arranged inseries with the reception antenna 50 and the automatic tuning assistcircuit 60. Specifically, the load 70 a is connected to a first terminal51 of the reception antenna 50.

A wireless power receiving apparatus 4 b shown in FIG. 17B includes athird transformer T3 by means of which a load 70 b is insulated from thereception antenna 50. The primary winding W1 of the third transformer T3is connected in series with the reception antenna 50. The load 70 b isconnected to the secondary winding W2 of the third transformer T3.

In a case in which the load is connected in series with the receptionantenna 50 as shown in FIGS. 17A and 17B, and in a case in which theload has a low impedance, such an arrangement has an advantage of acertain level of acquisition of electric power even without theadjustment by means of the automatic tuning assist circuit 60. However,such an arrangement has a disadvantage of a reduction of the Q-value ofthe reception antenna 50 due to the resistance component of the load.Thus, it is difficult for such an arrangement to acquire a large amountof electric power.

Conversely, in a case in which electric power is acquired from theautomatic tuning assist circuit 60 as shown in FIG. 14, the Q-value ofthe reception antenna 50 is not reduced due to the load 70. Thus, suchan arrangement is capable of acquiring a large amount of electric powereven in a case in which the load 70 has a high impedance. However, in acase in which the load 70 has a very low impedance, such an arrangementhas a problem of a reduction in the efficiency of the operation of theautomatic tuning assist circuit 60.

Thus, the position of the load in the circuit is preferably determinedgiving consideration to the electric power to be transmitted, theimpedance of the load, and so forth.

FIG. 18 is a circuit diagram showing a configuration of a wireless powerreceiving apparatus 4 c according to a third modification. An automatictuning assist circuit 60 c further includes a fourth auxiliary capacitorCA4 between the first terminal 61 and the second terminal 62 such thatit is connected in series with the fourth switch SW4. The position ofthe load 70 is not restricted in particular.

With such a modification, during the on time T_(ON3) of the third switchSW3, the correction voltage V_(A) is set to the capacitor voltageV_(CA3), and during the on time T_(ON4) of the fourth switch SW4, thecorrection voltage V_(A) is set to the capacitor voltage V_(CA4). Withthe wireless power receiving apparatus 4 c, the capacitor voltagesV_(CA1) and V_(CA2) can be optimized so as to provide a quasi-resonantstate in both the state in which f_(TX)>f_(c) and the state in whichf_(TX)<f_(c).

With such a wireless power receiving apparatus, the third switch SW3 andthe fourth switch SW4 may each be configured as a uni-directional switchor otherwise a bi-directional switch. In a case in which the thirdswitch SW3 and the fourth switch SW4 are each configured as auni-directional switch, there is a need to switch on and off the thirdswitch SW3 and the fourth switch SW4 with a phase such that no currentflows through each of the inversely conducting elements.

FIGS. 19A and 19B are circuit diagrams showing the configurations ofwireless power receiving apparatuses according to a fourth modificationand a fifth modification, respectively. The second control unit 64 isomitted from the diagrams.

With a wireless power receiving apparatus 4 d shown in FIG. 19A, anautomatic tuning assist circuit 60 d is coupled in series with thereception antenna 50 via a fourth transformer T4. Specifically, thesecondary winding W2 of the fourth transformer T4 is arranged betweenthe first terminal 61 and the second terminal 62. The primary winding W1of the fourth transformer T4 is arranged in series with the receptionantenna 50.

With the wireless power receiving apparatus 4 d, energy is transmittedand received between the reception antenna 50 and the automatic tuningassist circuit 60 d via the fourth transformer T4. Such an arrangementprovides the same advantages as those provided by the wireless powerreceiving apparatuses described above.

FIG. 19B shows an arrangement in which the load 70 is coupled with thereception antenna 50 and the automatic tuning assist circuit 60 d via afifth transformer T5. Specifically, the primary winding W1 of the fifthtransformer T5 is connected in series with the reception antenna 50. Theload 70 is connected between both ends of the secondary winding W2 ofthe fifth transformer T5.

Such an arrangement also provides the same advantages as those providedby the wireless power receiving apparatuses described above. With such awireless power receiving apparatus 4 e, the fourth transformer T4 may beomitted. With such an arrangement shown in FIG. 19A, the load 70 may becoupled with the third auxiliary capacitor C_(A3). Also, with such anarrangement shown in FIG. 19B, the load 70 may be coupled with the thirdcapacitor C_(A3) via a fifth transformer T5.

[Wireless Power Transmission System]

By combining the wireless power transmitting apparatus and the wirelesspower receiving apparatus described above, such an arrangement providesa wireless power transmission system.

FIG. 20 is a circuit diagram showing an example configuration of awireless power transmission system according to the first embodiment.The wireless power transmission system 1 includes the wireless powertransmitting apparatus 2 and the wireless power receiving apparatus 4.

The load 70 includes a rectifier circuit 72 and a switching regulator74, in addition to a load circuit 76. The rectifier circuit 72 isconfigured as a synchronous detector circuit, and includes a smoothingcapacitor C3, a third high-side switch SWH3, and a third low-side switchSWL3.

The switching regulator 74 is configured as a step-up converter, andcontrolled so as to be capable of supplying the load circuit 76 with themaximum electric power. The configuration and the operation of theswitching regulator 74 are known, and accordingly, description thereofwill be omitted.

The above is the configuration of the wireless power transmission system1. FIG. 21 is a waveform diagram showing the operation of the wirelesspower transmission system 1 shown in FIG. 20.

With the wireless power transmitting apparatus 2, the first switch SW1and the second switch SW2 are driven with a phase that is delayed byθ_(TX)=90 degrees with respect to the driving voltage V_(DRV). As aresult, the wireless power transmitting apparatus 2 provides aquasi-resonant state.

With the wireless power receiving apparatus 4, the third switch SW3 andthe fourth switch SW4 are driven with a phase that is delayed byθ_(RX)=180 degrees with respect to the driving voltage V_(DRV) employedon the wireless power transmitting apparatus 2 side. The third switchSW3 is driven with a phase that is delayed by 90 degrees with respect tothe first switch SW1. As a result, the wireless power receivingapparatus 4 also provides a quasi-resonant state.

The third high-side switch SWH3 and the third low-side switch SWL3 ofthe rectifier circuit 72 are driven with a phase that is delayed by 90degrees with respect to the third switch SW3 and the fourth switch SW4.As a result, a DC voltage is generated at the smoothing capacitor C3.The switching regulator 74 is configured to convert the DC voltage thusgenerated into an optimum voltage level for the load circuit 76.

The above is the operation of the wireless power transmission system 1.As described above, with the wireless power transmission system 1, thewireless power transmitting apparatus 2 and the wireless power receivingapparatus 4 each include an automatic tuning assist circuit. Thus, suchan arrangement allows the maximum electric power to be transmitted tothe load 70.

It is needless to say that any of the aforementioned wireless powertransmitting apparatuses 2 including the modifications may be combinedwith any of the aforementioned wireless power receiving apparatuses 4including the modifications.

Description has been made with reference to FIG. 20 regarding anarrangement in which an automatic tuning assist circuit is mounted onboth the wireless power transmitting apparatus 2 and the wireless powerreceiving apparatus 4. However, the present invention is not restrictedto such an arrangement.

Also, an arrangement may be made in which such an automatic tuningassist circuit is provided to only the wireless power transmittingapparatus 2, and the wireless power receiving apparatus is configured toadjust the resonance capacitor C_(RX) in the same way as withconventional techniques.

Conversely, an arrangement may be made in which such an automatic tuningassist circuit is provided to only the wireless power receivingapparatus 4, and the wireless power transmitting apparatus 2 isconfigured to adjust the resonance capacitor C_(TX) in the same way aswith conventional techniques.

Also, an arrangement may be made in which such an automatic tuningassist circuit is provided to only the wireless power transmittingapparatus 2, and the wireless power receiving apparatus 4 has noadjustment mechanism. Alternatively, an arrangement may be made in whichsuch an automatic tuning assist circuit is provided to only the wirelesspower receiving apparatus 4, and the wireless power transmittingapparatus 2 has no adjustment mechanism.

With such arrangements, tuning is performed by means of a singleautomatic tuning assist circuit so as to provide impedance matchingbetween the power supply 10 and the load 70, thereby providinghigh-efficiency electric power transmission. It is needless to say that,with such arrangements, the optimum value of the phase θ_(TX) (θ_(RX))of the switching of the automatic tuning assist circuit does not matchthe aforementioned values, i.e., 90 degrees or otherwise 270 degrees(180 degrees or otherwise 0 degrees).

Description has been made regarding the present invention with referenceto the first embodiment. The above-described embodiment has beendescribed for exemplary purposes only, and is by no means intended to beinterpreted restrictively. Rather, it can be readily conceived by thoseskilled in this art that various modifications may be made by makingvarious combinations of the aforementioned components or processes,which are also encompassed in the technical scope of the presentinvention. Description will be made below regarding such modifications.

With the wireless power transmitting apparatus 2 including the automatictuning assist circuit 30, in some cases, such an arrangement is capableof providing a quasi-resonant state even without including the resonancecapacitor C_(TX). In this case, such a resonance capacitor C_(TX) may beomitted. In the same way, an arrangement may be made in which thewireless power receiving apparatus 4 including the automatic tuningassist circuit 60 does not include the resonance capacitor C_(RX).

The wireless power transmitting apparatus 2 is configured to encrypt theelectric power signal S1 by changing at least one of the frequencyf_(TX) and the phase of the driving voltage V_(DRV) according to apredetermined rule (encryption code). In a case in which the wirelesspower receiving apparatus 4 knows the encryption code, the wirelesspower receiving apparatus 4 controls the switching frequency and phaseof the automatic tuning assist circuit 60 based on the encryption code.As a result, even if the electric power signal S1 is encrypted, such anarrangement is capable of decrypting the electric power signal S1 andreceiving the power supply. In a case in which a wireless powerreceiving apparatus does not know the encryption code, the wirelesspower receiving apparatus cannot appropriately control the switchingoperation of the automatic tuning assist circuit 60. Thus, such awireless power receiving apparatus cannot receive electric power. Withwireless power transmission, there is a problem of potential power theftby malicious users. However, by employing such an automatic tuningassist circuit, such a problem can be solved.

Also, in a case in which a single wireless power transmitting apparatus2 supplies electric power to multiple wireless power receivingapparatuses 4, by employing such an automatic tuning assist circuit,such an arrangement is capable of controlling the amount of electricpower to be supplied to each terminal.

[Second Embodiment]

Description has been made in the first embodiment regarding theautomatic tuning assist circuit including the two switches SW1 and SW2.An automatic tuning assist circuit according to a second embodiment hasa configuration including four switches. The automatic tuning assistcircuit according to the second embodiment has the same blockconfiguration as that of the first embodiment except for the automatictuning assist circuit 80. Also, various kinds of modifications asdescribed in the first embodiment may effectively be made for the secondembodiment.

[Wireless Power Transmitting Apparatus]

FIG. 22 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus 6 according to a second embodiment. The wirelesspower transmitting apparatus 6 is configured to transmit an electricpower signal S1 to a wireless power receiving apparatus (not shown). Theelectric power signal S1 is configured using the near-field components(electric field, magnetic field, or electromagnetic field) ofelectromagnetic waves that have not yet become radio waves.

The wireless power transmitting apparatus 6 includes a power supply 10,a transmission antenna 20, an automatic tuning assist circuit 80, and afirst control unit 40.

The transmission antenna 20 includes a transmission coil L_(TX) arrangedbetween its first terminal 21 and its second terminal 22. A resonancecapacitor C_(TX) is arranged in series with the transmission coilL_(TX). The resonance capacitor C_(TX) and the transmission coil L_(TX)may also be mutually exchanged.

The automatic tuning assist circuit 80 is coupled in series with thetransmission antenna 20. The power supply 10 is configured as ahalf-bridge circuit in the same way as shown in FIG. 2. The power supply10 is configured to apply an AC driving voltage V_(DRV) having apredetermined transmission frequency f_(TX) between the respectiveterminals of the circuit that comprises the transmission antenna 20 andthe automatic tuning assist circuit 80. The driving voltage V_(DRV) maybe configured to have a desired AC waveform, examples of which include arectangular waveform, a trapezoidal waveform, a sine waveform, and thelike. With the present embodiment, the driving voltage V_(DRV) isconfigured as a rectangular wave signal which swings between a firstvoltage level (power supply voltage V_(DD)) and a second voltage level(ground voltage V_(GND)=0 V).

The power supply 10 is configured as a half-bridge circuit, as with thepower supply 10 shown in FIG. 2. The first control unit 40 is configuredto switch on and off the first high-side switch SWH1 and the firstlow-side switch SWL1 in a complementary manner, with a transmissionfrequency f_(Tx).

With the second embodiment, the automatic tuning assist circuit 80includes a first terminal 81, a second terminal 82, a first switch SWc1through a fourth switch SWc4, and a first auxiliary capacitor C_(A5).

The first switch SWc1 and the second switch SWc2 are sequentiallyarranged in series between the first terminal 81 and the second terminal82. The third switch SWc3 and the fourth switch SWc4 are sequentiallyarranged between the first terminal 81 and the second terminal 82, andare arranged in parallel with the first switch SWc1 and the secondswitch SWc2. The first auxiliary capacitor C_(A5) is arranged between aconnection node N1 that connects the first switch SWc1 and the secondswitch SWc2 and a connection node N2 that connects the third switch SWc3and the fourth switch SWc4. The first auxiliary capacitor C_(A5) ispreferably configured to have a capacitance that is sufficiently greaterthan that of the resonance capacitor C_(TX).

The first control unit 40 is configured to switch on and off the firstswitch SWc1 through the fourth switch SWc4 in a complementary manner,with the same frequency fTx as that of the driving voltage V_(DRV), andwith a predetermined phase difference θ_(TX) with respect to the drivingvoltage V_(DRV). The phase difference θ_(TX) is preferably set to avalue in the vicinity of +90 degrees or otherwise −90 degrees (270degrees). That is to say, a part of the first control unit 40 functionsas a component of the automatic tuning assist circuit 80.

In the same way as with the first embodiment, the first switch SWc1through the fourth switch SWc4 may each be configured as auni-directional switch or otherwise a bi-directional switch. In a casein which the first switch SWc1 through the fourth switch SWc4 are eachconfigured as a uni-directional switch, there is a need to pay attentionto their switching phases, as described above in the first embodiment.

The above is the configuration of the wireless power transmittingapparatus 6. Next, description will be made regarding the operationthereof.

FIG. 23 is a waveform diagram showing the operation of the wirelesspower transmitting apparatus 6 shown in FIG. 22. FIG. 23 shows, in thefollowing order beginning from the top, the voltage at the firsthigh-side switch SWH1, the voltage at the first low-side switch SWL1,the driving voltage V_(DRV), the voltage at the first switch SWc1, thevoltage at the second switch SWc2, the voltage at the third switch SWc3,the voltage at the fourth switch SWc4, the correction voltage V_(A)generated at the first terminal 81, the resonance current I_(TX) thatflows through the transmission antenna 20, and the resonance voltageV_(TX) that develops across the transmission coil L_(TX) and theresonance capacitor C_(TX). In the waveform diagram for each switch, thehigh level represents the on state, and the low level represents the offstate. It should be noted that FIG. 23 shows the waveforms of theresonance current I_(TX) and the resonance voltage V_(TX) obtained aftera sufficient time has elapsed after the automatic tuning assist circuit80 starts to operate.

As shown in FIG. 23, by switching on and off the first high-side switchSWH1 and the first low-side switch SWL1 in a complementary manner, suchan arrangement is capable of generating the driving voltage V_(DRV)having a rectangular waveform. The driving voltage V_(DRV) thusgenerated is applied across the transmission antenna 20 and theautomatic tuning assist circuit 80. The first control unit 40 isconfigured to drive a first pair P1 comprising the first switch SWc1 andthe fourth switch SWc4 with the same frequency as that of the drivingvoltage V_(DRV), and with a phase that is delayed by θ_(TX) (=90degrees) with respect to the driving voltage V_(DRV). Furthermore, thefirst control unit 40 is configured to drive a second pair P2 comprisingthe second switch SWc2 and the third switch SWc3 in a complementarymanner with respect to the first pair P1, i.e., with a phase that isshifted by 180 degrees with respect to that of the first pair P1.

During the on time Tom of the first pair P1, the resonance currentI_(TX) flows through a path including the first switch SWc1, the firstauxiliary capacitor C_(A5), and the fourth switch SWc4. During the ontime T_(ON2) of the second pair P2, the resonance current I_(TX) flowsthrough a path including the third switch SWc3, the first auxiliarycapacitor C_(A5), and the second switch SWc2.

That is to say, the first auxiliary capacitor C_(A5) is charged anddischarged by means of the resonance current I_(TX). As a result, thecapacitor voltage V_(CA5) develops at the first auxiliary capacitorC_(A5).

The automatic tuning assist circuit 80 is configured to apply acorrection voltage V_(A) to the second terminal 22 of the transmissionantenna 20. During the on time T_(ON1) of the first pair P1, thecorrection voltage V_(A) is set to a first polarity. During the on timeT_(ON2) of the second pair P2, the correction voltage V_(A) is set to asecond polarity. The automatic tuning assist circuit 80 can be regardedas a correction power supply configured to apply the correction voltageV_(A) to the transmission antenna 20. That is to say, it can be clearlyunderstood that the wireless power transmitting apparatus 6 can berepresented by the same equivalent circuit as that shown in FIG. 5, andis configured to operate according to the same operation mechanism.

That is to say, in a case in which the automatic tuning assist circuit80 operates, the correction voltage V_(A) is applied to the transmissionantenna 20 with a phase that is delayed by θ_(TX)=90 degrees withrespect to the driving voltage V_(DRV). As a result, phase matching isobtained between the resonance current I_(TX) and the driving voltageV_(DRV), thereby providing a quasi-resonant state. In this state, theresonance current I_(TX) has a greater amplitude than that in thenon-resonant state. This is as shown in the phasor diagrams in FIGS. 7and 9.

The operation of the automatic tuning assist circuit 80 according to thesecond embodiment is the same as described in the first embodiment withreference to FIG. 8. Thus, such an arrangement is capable ofautomatically generating the correction voltage V_(A) which provides aquasi-resonant state.

The above is the operation of the wireless power transmitting apparatus6.

As described above, without adjusting the resonance frequency f_(c) ofthe transmission antenna 20, the wireless power transmitting apparatus 6is capable of automatically tuning the circuit state so as to providethe quasi-resonant state. In the wireless power transmission, theresonance frequency changes over time according to the position relationbetween the wireless power transmitting apparatus and the wireless powerreceiving apparatus. The wireless power transmitting apparatus 6 iscapable of following the change in the resonance frequency with highspeed, thereby providing high-efficiency electric power transmission.

Furthermore, in a case in which a large amount of electric power istransmitted by means of wireless power transmission, a very high voltagedevelops between both ends of the resonance capacitor C_(TX), whichlimits the use of a variable capacitor. With the wireless powertransmitting apparatus 6, there is no need to adjust the capacitance ofthe resonance capacitor C_(TX). Thus, such an arrangement does notrequire such a variable capacitor or the like, which is anotheradvantage.

Description has been made above regarding an arrangement in which thefirst pair comprising the first switch SWc1 and the fourth switch SWc4is switched on and off with a phase that is delayed by θ_(TX) (=90degrees) with respect to the phase of the switching of the firsthigh-side switch SWH1 (driving voltage V_(DRV)). However, the phasedifference θ_(TX) between the first pair and the first high-side switchSWH1 is not restricted to 90 degrees. Also, an arrangement may be madein which the phase difference θ_(TX) between the first pair and thefirst high-side switch SWH1 is set to 270 degrees (−90 degrees). In thiscase, the capacitor voltage V_(CA1) is automatically adjusted such thatthe polarity reverses. In a case in which the first switch SWc1 throughthe fourth switch SWc4 are each configured as a uni-directional switch,there is a need to switch on and off the first switch SWc1 through thefourth switch SWc4 with a phase such that no current flows through eachof the inversely conducting elements. Specifically, in a case in whichf_(c)<f_(TX), the phase difference θ_(TX) is preferably set to 90degrees. Conversely, in a case in which f_(c)>f_(TX), the phasedifference θ_(TX) is preferably set to 270 degrees.

Also, the phase difference θ_(TX) may be moved away from 90 degrees or270 degrees, as described in the first embodiment.

Next, description will be made regarding modifications of the wirelesspower transmitting apparatus 6. Each modification may be combined withany one of the other modifications, which is encompassed within thescope of the present invention.

Description has been made above regarding an arrangement in which thefirst control unit 40 drives multiple switches included in the automatictuning assist circuit 80 with the same frequency f_(TX) as that of thedriving voltage V_(DRV). However, the present invention is notrestricted to such an arrangement. Also, the first control unit 40 maybe configured to switch on and off the aforementioned switches with afrequency obtained by multiplying or dividing the frequency of thedriving voltage V_(DRV) by an odd number. Such an arrangement alsoprovides a quasi-resonant state.

FIG. 24 is a circuit diagram showing a configuration of a wireless powertransmitting apparatus 6 a according to a first modification. A powersupply 10 c shown in FIG. 24 is configured as an H-bridge circuit. Atransmission antenna 20 and an automatic tuning assist circuit 80 a arearranged in series between a first output terminal OUT1 and a secondoutput terminal OUT2 of a power supply 10 c. Furthermore, a capacitor C2configured to block DC current is arranged in series with thetransmission antenna 20 and the automatic tuning assist circuit 80 a.With the automatic tuning assist circuit 80 a, one end (N2) of a firstauxiliary capacitor C_(A5) is grounded.

With the wireless power transmitting apparatus 6 a shown in FIG. 24,such an arrangement provides the same advantages as those provided bythe wireless power transmitting apparatuses described above.

As described in the first embodiment, the power supply, the automatictuning assist circuit, or otherwise both of them, may be coupled withthe transmission antenna 20 via a transformer. FIGS. 25A through 25C arecircuit diagrams respectively showing the configurations of wirelesspower transmitting apparatuses 6 b through 6 d according to secondthrough fourth modifications. The first control unit 40 is not shown.

With the wireless power transmitting apparatus 6 b shown in FIG. 25A,the automatic tuning assist circuit 80 a is coupled in series with thetransmission antenna 20 via a sixth transformer T6. Specifically, thesixth transformer T6 is configured to have a primary winding W1connected in series with the transmission antenna 20, and to have asecondary winding W2 connected between the first terminal 61 and thesecond terminal 62 of the automatic tuning assist circuit 80 a. Thepower supply 10 c is configured to apply a driving voltage across aseries circuit that comprises the transmission antenna 20 and theprimary winding W1 of the sixth transformer T6.

With a wireless power transmitting apparatus 6 c shown in FIG. 25B, thepower supply 10 c is coupled with the transmission antenna 20 and theautomatic tuning assist circuit 80 a via a seventh transformer T7. Thepower supply 10 c is configured to apply a driving voltage across theprimary winding W1 of the seventh transformer T7. The transmissionantenna 20 and the automatic tuning assist circuit 80 a are arranged inseries with the secondary winding W2.

With a wireless power transmitting apparatus 6 d shown in FIG. 25C, thepower supply 10 having a half-bridge configuration is coupled with thetransmission antenna 20 and the automatic tuning assist circuit 80 a viathe seventh transformer T7. A capacitor C3 configured to block DCcurrent is arranged between the output terminal of the power supply 10and the primary winding W1 of the seventh transformer T7.

Also, the modifications shown in FIGS. 25A through 25C may be combined.That is to say, both the power supply and the automatic tuning assistcircuit may be coupled with the transmission antenna via a transformer.

Such modifications also provide the same advantages provided by thewireless power transmitting apparatuses described above.

[Wireless power receiving apparatus]

The automatic tuning assist circuit according to the second embodimentdescribed above may be employed in a wireless power receiving apparatus.Description will be made below regarding such a wireless power receivingapparatus.

FIG. 26 is a circuit diagram showing a wireless power receivingapparatus 8 according to the second embodiment. The wireless powerreceiving apparatus 8 is configured to receive the electric power signalS1 transmitted from the aforementioned wireless power transmittingapparatus or otherwise a wireless power transmitting apparatus having anentirely different configuration. The electric power signal S1 isconfigured using the near-field components (electric field, magneticfield, or electromagnetic field) of electromagnetic waves that have notyet become radio waves.

The wireless power receiving apparatus 8 includes a reception antenna50, an automatic tuning assist circuit 90, and a load 70 to be suppliedwith electric power. The load 70 may include an unshown rectifiercircuit, detector circuit, or the like, as a built-in component.

The reception antenna 50 includes a reception coil L_(RX) and aresonance capacitor C_(RX) arranged in series between a first terminal51 and a second terminal 52.

The automatic tuning assist circuit 90 has the same configuration asthat of the automatic tuning assist circuit 80 shown in FIG. 22.Specifically, the automatic tuning assist circuit 90 includes a firstterminal 91, a fifth switch SWc5 through an eighth switch SWc8, and asecond auxiliary capacitor C_(A6).

The fifth switch SWc5 and the sixth switch SWc6 are arranged in seriesbetween the first terminal 91 and the second terminal 92. The seventhswitch SWc7 and the eighth switch SWc8 are sequentially arranged inseries between the first terminal 91 and the second terminal 92.Furthermore, the seventh switch SWc7 and the eighth switch SWc8 arearranged in parallel with the fifth switch SWc5 and the sixth switchSWc6. The second auxiliary capacitor C_(A6) is arranged between aconnection node N3 that connects the fifth switch SWc5 and the sixthswitch SWc6 and a connection node N4 that connects the seventh switchSWc7 and the eighth switch SWc8. The second auxiliary capacitor C_(A6)is preferably configured to have a sufficiently great capacitance ascompared with the resonance capacitance C_(RX).

A second control unit 94 is configured to switch on and off the fifthswitch SWc5 through the eighth switch SWc8 with the same frequency asthat of the electric power signal S1, and with a phase difference θ_(RX)with respect to the driving voltage (V_(DRV)) which is applied to thetransmitter-side antenna. For example, the phase difference θ_(RX) ispreferably set to 180 degrees or otherwise 0 degrees.

The automatic tuning assist circuit 90 is coupled in series with thereception antenna 50. Furthermore, the load 70 to be supplied withelectric power is directly connected with the reception antenna 50 andthe automatic tuning assist circuit 90.

The above is the configuration of the wireless power receiving apparatus8. Next, description will be made regarding the operation thereof. Thewireless power receiving apparatus 8 can be represented by the sameequivalent circuit diagram as that which represents the wireless powerreceiving apparatus 4 shown in FIG. 15. As with the automatic tuningassist circuit 80 of the wireless power transmitting apparatus 6, theautomatic tuning assist circuit 90 can be regarded as a correction powersupply configured to apply a correction voltage V_(A) to the receptionantenna 50.

FIG. 27 is a waveform diagram showing the operation of the wirelesspower receiving apparatus 8 shown in FIG. 26. FIG. 27 shows the voltagesapplied to the fifth switch SWc5 through the eighth switch SWc8, thecorrection voltage V_(A), the resonance current I_(RX) that flowsthrough the reception antenna 50, and the resonance voltage V_(RX) thatdevelops across the reception coil L_(RX) and the resonance capacitorC_(RX). In the waveform diagrams showing the voltages applied to therespective switches, the high-level state represents the on state, andthe low-level state represents the off state.

A first pair comprising the fifth switch SWc5 and the eighth switch SWc8is switched on and off with a phase θ_(RX) which is shifted by 180degrees or otherwise 0 degrees with respect to the driving voltageV_(DRV) of the wireless power transmitting apparatus side. A second paircomprising the sixth switch SWc6 and the seventh switch SWc7 is switchedon and off in a complementary manner with respect to the first pair.During the on time T_(ON1) of the first pair, the resonance currentI_(RX) flows through a path comprising the fifth switch SWc5, the secondauxiliary capacitor C_(A6), and the eighth switch SWc8. During the ontime T_(ON2) of the second pair, the resonance current I_(RX) flowsthrough a path comprising the sixth switch SWc6, the second auxiliarycapacitor C_(A6), and the seventh switch SWc7.

The second auxiliary capacitor C_(A6) is charged and discharged by meansof the resonance current I_(RX). As a result, a capacitor voltageV_(CA6) develops at the capacitor C_(A6). With such an arrangement, thecorrection voltage V_(A) that corresponds to the capacitor voltageV_(CA6) is applied to the reception antenna 50. Thus, such anarrangement allows the resonance current I_(A) to have a phase thatmatches the phase of the driving voltage V_(DRV) that is used in thetransmitter side, thereby providing a quasi-resonant state.

In order to provide a quasi-resonant state, there is a need to switch onand off the fifth switch SWc5 and the eighth switch SWc8 with a suitablefrequency f_(TX) and with a suitable phase θ_(RX). In order to meet thisrequirement, the wireless power transmitting apparatus may be configuredto transmit the data which represents the frequency f_(TX) and the phaseθ_(RX) to the wireless power receiving apparatus 8. Also, the wirelesspower receiving apparatus 8 may be configured to sweep the phase θ_(RX)so as to detect the optimum phase θ_(RX).

The above is the operation of the wireless power receiving apparatus 8.

As described above, with the wireless power receiving apparatus 8 shownin FIG. 26, such an arrangement automatically provides a resonant statewithout a need to adjust the capacitance of the resonance capacitorC_(RX).

Next, description will be made regarding modifications of the wirelesspower receiving apparatus 8.

Description has been made above regarding an arrangement in which thesecond control unit 64 drives the multiple switches, which arecomponents of the automatic tuning assist circuit 30, with the samefrequency as that of the electric power signal S1. However, the presentinvention is not restricted to such an arrangement. Also, the secondcontrol unit 64 may be configured to switch on and off theaforementioned switches with a frequency obtained by multiplying ordividing the frequency of the electric power signal S1 by an odd number.Such an arrangement also provides a quasi-resonant state.

Description has been made with reference to FIG. 26 regarding anarrangement in which one terminal of the load 70 is grounded, and theground potential is used as the reference potential. Also, instead ofsuch an arrangement in which one terminal of the load 70 is grounded,one terminal of the second auxiliary capacitor C_(A6) of the automatictuning assist circuit 90, i.e., either the connection node N3 or N4, maybe grounded.

FIGS. 28A and 28B are circuit diagrams showing the configurations ofwireless power receiving apparatuses according to a second modificationand a third modification.

Description has been made with reference to FIG. 26 regarding anarrangement in which the load 70 is connected in series with thereception antenna 50. Also, the load 70 may be arranged at a differentposition.

With a wireless power receiving apparatus 8 a according to a firstmodification shown in FIG. 28A, the connection node N4 of the automatictuning assist circuit 90 a is grounded. A load 70 a is arranged inparallel with the second auxiliary capacitor C_(A6). That is to say, theload 70 a is supplied with a capacitor voltage V_(CA6) that develops atthe second auxiliary capacitor C_(A6).

With a wireless power receiving apparatus 8 b according to a secondmodification shown in FIG. 28B, a load 70 b is coupled via an eighthtransformer T8 with a series circuit comprising the reception antenna 50and the automatic tuning assist circuit 90 a.

FIGS. 28C and 28D are circuit diagrams each showing an exampleconfiguration of such a load. A load 70 c shown in FIG. 28C includes adiode rectifier circuit 72 c and a load circuit 76. A load 70 d shown inFIG. 28D includes a synchronous detector circuit 72 d and the loadcircuit 76. Such a load circuit may further include a switchingregulator 74 as shown in FIG. 20.

Such an automatic tuning assist circuit 90 may be coupled in series withthe reception antenna 50 via a transformer. FIG. 29 is a circuit diagramshowing a configuration of a wireless power receiving apparatus 8 caccording to a third modification. The automatic tuning assist circuit90 a is coupled in series with the reception antenna 50 via a ninthtransformer T9. A load may be arranged in series with the receptionantenna 50 and the primary winding W1. Also, such a load may be arrangedin parallel with the second auxiliary capacitor C_(A6).

Such modifications also provide the same advantages as those provided bythe wireless power receiving apparatus 8 shown in FIG. 26.

In a case in which the load is connected in series with the receptionantenna 50 as shown in FIG. 26, and in a case in which the load has alow impedance, such an arrangement has an advantage of a certain levelof acquisition of electric power even without the adjustment by means ofthe automatic tuning assist circuit 90. However, such an arrangement hasa disadvantage of a reduction of the Q-value of the reception antenna 50due to the resistance component of the load. Thus, it is difficult forsuch an arrangement to acquire a large amount of electric power.

Conversely, in a case in which electric power is acquired from theautomatic tuning assist circuit 90 a as shown in FIG. 28A, the Q-valueof the reception antenna 50 is not reduced due to the load 70. Thus,such an arrangement is capable of acquiring a large amount of electricpower even in a case in which the load 70 a has a high impedance.However, in a case in which the load 70 a has a very low impedance, suchan arrangement has a problem of a reduction in the efficiency of theoperation of the automatic tuning assist circuit 60.

Thus, the position of the load in the circuit is preferably determinedgiving consideration to the electric power to be transmitted, theimpedance of the load, and so forth.

The fifth switch SWc5 through the eighth switch SWc8 may each beconfigured as a uni-directional switch or otherwise a bi-directionalswitch. As described above, in a case in which these switches are eachconfigured as a uni-directional switch, there is a need to pay attentionto their switching phases.

[Wireless Power Transmission System]

By combining the wireless power transmitting apparatus 6 and thewireless power receiving apparatus 8 described in the second embodiment,such an arrangement provides a wireless power transmission system.

Description has been made regarding an arrangement in which an automatictuning assist circuit is mounted on each of the wireless powertransmitting apparatus 6 and the wireless power receiving apparatus 8.However, the present invention is not restricted to such an arrangement.

Also, an arrangement may be made in which such an automatic tuningassist circuit is provided to only the wireless power transmittingapparatus 6, and the wireless power receiving apparatus adjusts theresonance capacitor C_(RX) in the same way as with conventionaltechniques. Conversely, an arrangement may be made in which such anautomatic tuning assist circuit is provided to only the wireless powerreceiving apparatus 8, and the wireless power transmitting apparatus 6adjusts the resonance capacitor C_(TX) in the same way as withconventional techniques.

Also, an arrangement may be made in which such an automatic tuningassist circuit is provided to only the wireless power transmittingapparatus 6, and the wireless power receiving apparatus 8 has noadjustment mechanism. Alternatively, an arrangement may be made in whichsuch an automatic tuning assist circuit is provided to only the wirelesspower receiving apparatus 8, and the wireless power transmittingapparatus 6 has no adjustment mechanism.

With such arrangements, tuning is performed by means of a singleautomatic tuning assist circuit so as to provide impedance matchingbetween the power supply 10 and the load 70, thereby providinghigh-efficiency electric power transmission. It should be noted that,with such arrangements, the optimum value of the phase θ_(TX) (θ_(RX))of the switching of the automatic tuning assist circuit does not matchthe aforementioned values, i.e., 90 degrees or otherwise 270 degrees(180 degrees or otherwise 0 degrees).

Also, the wireless power transmitting apparatus 2 according to the firstembodiment may be combined with the wireless power receiving apparatus 8according to the second embodiment. Also, the wireless power receivingapparatus 4 according to the first embodiment may be combined with thewireless power transmitting apparatus 6 according to the secondembodiment.

Description has been made regarding the present invention with referenceto the second embodiment. The above-described embodiment has beendescribed for exemplary purposes only, and is by no means intended to beinterpreted restrictively. Rather, it can be readily conceived by thoseskilled in this art that various modifications may be made by makingvarious combinations of the aforementioned components or processes,which are also encompassed in the technical scope of the presentinvention. Description will be made below regarding such modifications.

With the wireless power transmitting apparatus 6 including the automatictuning assist circuit 80, in some cases, such an arrangement is capableof providing a quasi-resonant state even while omitting the resonancecapacitor C_(TX). In this case, such a resonance capacitor C_(TX) may beomitted. In the same way, an arrangement may be made in which thewireless power receiving apparatus 8 including the automatic tuningassist circuit 90 does not include the resonance capacitor C_(RX).

The wireless power transmitting apparatus 6 is configured to encrypt theelectric power signal S1 by changing at least one of the frequencyf_(TX) and the phase of the driving voltage V_(DRV) according to apredetermined rule (encryption code). In a case in which the wirelesspower receiving apparatus 8 knows the encryption code, the wirelesspower receiving apparatus 8 controls the switching frequency and phaseof the automatic tuning assist circuit 90 based on the encryption code.As a result, even if the electric power signal S1 is encrypted, such anarrangement is capable of decrypting the electric power signal S1 andreceiving the power supply. In a case in which the wireless powerreceiving apparatus does not know the encryption code, the wirelesspower receiving apparatus cannot appropriately control the switchingoperation of the automatic tuning assist circuit 90. Thus, such awireless power receiving apparatus cannot receive electric power. Withwireless power transmission, there is a problem of potential power theftby malicious users. However, by employing such an automatic tuningassist circuit, such a problem can be solved.

Also, in a case in which a single wireless power transmitting apparatus6 supplies electric power to multiple wireless power receivingapparatuses 8, by employing such an automatic tuning assist circuit,such an arrangement is capable of controlling the amount of electricpower to be supplied to each terminal.

The usage of the automatic tuning assist circuit 30 is not restricted tosuch wireless power transmission. Rather, the present invention isapplicable to various kinds of applications which require tuning.

Description has been made regarding the present invention with referenceto the embodiments. However, the above-described embodiments show onlythe mechanisms and applications of the present invention for exemplarypurposes only, and are by no means intended to be interpretedrestrictively. Rather, various modifications and various changes in thelayout can be made without departing from the spirit and scope of thepresent invention defined in appended claims.

What is claimed is:
 1. A wireless power receiving apparatus configuredto receive an electric power signal transmitted from a wireless powertransmitting apparatus, the wireless power receiving apparatuscomprising: a reception antenna comprising a reception coil and aresonance capacitor connected in series; and an automatic tuning assistcircuit coupled with the reception antenna; wherein the automatic tuningassist circuit comprises: a first terminal; a second terminal; N (Nrepresents an integer) auxiliary capacitors; a plurality of switches,each of which is arranged between two terminals from among the firstterminal, the second terminal, and the terminals of the N auxiliarycapacitors; and a second control unit configured to switch on and offthe plurality of switches, wherein a periodic voltage occurs across eachof the N auxiliary capacitors, and wherein the automatic tuning assistcircuit comprises: a third switch and a third auxiliary capacitorarranged in series between the first terminal and the second terminal;and a fourth switch arranged between the first terminal and the secondterminal such that it is arranged in parallel with the third switch andthe third auxiliary capacitor.
 2. The wireless power receiving apparatusaccording to claim 1, wherein the second control unit is configured toswitch on and off each of the plurality of switches with the samefrequency as that of the electric power signal, or otherwise with afrequency obtained by multiplying or dividing the frequency of theelectric power signal by an odd number.
 3. The wireless powertransmitting apparatus according to claim 1, wherein the second controlunit is configured to switch on and off the third switch and the fourthswitch with the same frequency as that of the electric power signal. 4.The wireless power receiving apparatus according to claim 1, wherein thesecond control unit is configured to drive the third switch and thefourth switch with a predetermined phase difference with respect to thedriving voltage applied to the transmission antenna of the wirelesspower transmitting apparatus.
 5. The wireless power receiving apparatusaccording to claim 1, wherein the automatic tuning assist circuitfurther comprises a fourth auxiliary capacitor between the firstterminal and the second terminal such that it is arranged in series withthe fourth switch.
 6. The wireless power receiving apparatus accordingto claim 1, wherein the third switch and the fourth switch are eachconfigured as a uni-directional switch, and wherein the second controlunit is configured to switch on and off the third switch and the fourthswitch with a phase controlled such that no current flows through eachof their inversely conducting elements.
 7. The wireless power receivingapparatus according to claim 1, wherein the third switch and the fourthswitch are each configured as a bi-directional switch.
 8. The wirelesspower receiving apparatus according to claim 1, wherein a load to besupplied with electric power is coupled across the third auxiliarycapacitor.
 9. The wireless power receiving apparatus according to claim1, wherein a load to be supplied with electric power is coupled inseries to the reception antenna.
 10. A wireless power supply systemcomprising: a wireless power transmitting apparatus configured totransmit an electric power signal; and wireless power receivingapparatus according to claim 1, configured to receive the electric powersignal.
 11. A wireless power receiving apparatus configured to receivean electric power signal transmitted from a wireless power transmittingapparatus, the wireless power receiving apparatus comprising: areception antenna comprising a reception coil and a resonance capacitorconnected in series; and an automatic tuning assist circuit coupled withthe reception antenna; wherein the automatic tuning assist circuitcomprises: a first terminal; a second terminal; N (N represents aninteger) auxiliary capacitors; a plurality of switches, each of which isarranged between two terminals from among the first terminal, the secondterminal, and the terminals of the N auxiliary capacitors; and a secondcontrol unit configured to switch on and off the plurality of switches,wherein a periodic voltage occurs across each of the N auxiliarycapacitors, wherein the wireless power receiving apparatus furthercomprises a transformer having a primary winding connected in serieswith the reception antenna, and wherein a load to be supplied withelectric power is connected to a secondary winding of the transformer.12. A wireless power receiving apparatus configured to receive anelectric power signal transmitted from a wireless power transmittingapparatus, the wireless power receiving apparatus comprising: areception antenna comprising a reception coil and a resonance capacitorconnected in series; and an automatic tuning assist circuit coupled withthe reception antenna; wherein the automatic tuning assist circuitcomprises: a first terminal; a second terminal; N (N represents aninteger) auxiliary capacitors; a plurality of switches, each of which isarranged between two terminals from among the first terminal, the secondterminal, and the terminals of the N auxiliary capacitors; and a secondcontrol unit configured to switch on and off the plurality of switches,wherein a periodic voltage occurs across each of the N auxiliarycapacitors, and wherein the automatic tuning assist circuit is coupledin series with the reception antenna via a transformer.